This invention relates to crystalline aromatic polyketones having thioether groups and a process for producing the same. More particularly, this invention relates to crystalline aromatic polyketones having a chemical structure comprising phenylene groups bonded via an ether group, a thioether group and a ketone group, or via a thioether group and a ketone group, and having excellent heat resistance, fire retardant properties, solvent resistance, mechanical properties, thermoplastic moldability, and the like, and a process for industrially producing the same.
As polymers having a structure comprising phenylene groups bonded via an ether group and a ketone group, there have been known polymers having repeating units of the formula: ##STR3## and repeating units of the formula: ##STR4## Since these polymers are excellent heat resistance, molding stability and mechanical strength, they have been regarded as useful for molding materials.
These polymers have a defect in that their starting materials are difficult to obtain, so that there has not been known a process suitable for producing these polymers on a large scale.
For example, high molecular-weight aromatic polyetherketones having repeating units of the formula (2) are produced by a condensation reaction of a dihalobenzophenone and hydroquinone. In order to produce polymers having practically usable physical and chemical properties, it is necessary to use difluorobenzophenone as the dihalobenzophenone (e.g. U.S. Pat. No. 4,320,224), which inevitably results in making the raw material cost high.
There is also known a process for producing polyetherthioethers from an alkali metal salt of hydroxythiophenol and an aromatic dihalide such as dichlorodiphenylsulfone (British Patent No. 1,295,584), but the resulting polymer is amorphous due to an internal structure of irregular arrangement of repeating units and not always satisfactory as to heat resistance, solvent resistance and mechanical properties.
There is also proposed a process for producing polyethers or polythioethers from a compound having two --XH groups (wherein X is an oxygen atom or a sulfur atom) and a dihalobenzenoid compound in the presence of potassium carbonate (British Patent No. 1,264,900). But the polymerization temperature is low and no crystalline polymer is obtained according to this process like the above-mentioned case.
On the other hand, as polymers having a structure comprising phenylene groups bonded via a thioether group, there has been known a polyphenylenesulfide having repeating units of the formula: ##STR5## obtained by reacting, for example, dichlorobenzene and sodium sulfide (U.S. Pat. No. 3,919,177).
This polyphenylenesulfide has properties such as excellent fire retardant properties, low moisture absorption properties, high dimensional stability, good affinity to an inorganic filler and high mixing concentration of the filler. But since this polyphenylenesulfide has a glass transition temperature (Tg) of as low as 80.degree. C., the heat distortion temperature (HDT) is low when no glass fiber is filled and thus there is a problem with regard to heat resistance. Further, since the crystalline melting point (Tm) of this polymer is relatively low as at about 281.degree. C., the applications of this polymer as a heat resistant polymer are limited.
Therefore, the development of these kinds of polymers having a higher crystalline melting point has been desired.
In order to make the melting point of these kinds of polymers higher, there have been proposed various processes. For example, it is proposed to introduce units of the formula: ##STR6## between linkages of ##STR7## (U.S. Pat. No. 4,286,018). But the resulting polymer has a defect in that the crystallinity is lowered to deteriorate the heat resistant and mechanical properties compared with the homopolymer, when the content of the unit of the formula: ##STR8## is 90% by mole or less.
As polymers obtained by regularly introducing ketone groups into polyphenylenesulfides, there are known polymers having repeating units of the formula: ##STR9## and repeating units of the formula: ##STR10## But the polymer having the repeating units of the formula (4) melts at 220.degree. to 230.degree. C. (U.S. Pat. No. 3,432,468) and is insufficient in heat resistance. On the other hand, the polymer having the repeating units of the formula (5) has a Tm as high as 352.degree. C., but there is a problem in that the resulting film is brittle (British Patent No. 1,368,967).
As mentioned above, polymers having improved heat resistance by enhancing Tg and Tm without losing the excellent properties of polyphenylenesulfides have not been discovered.
These polymers such as those having repeating units of the formula (4) are generally obtained by reacting dipotassium salt of 4,4'-disulfhydryldiphenylsulfide and 4,4'-dibromobenzophenone at a temperature of 130.degree. to 150.degree. C. But under such low temperature polymerization conditions, since a low molecular-weight polymer is deposited at an initial stage of the polymerization, it is very difficult to obtain the desired highly crystalline high molecular weight polymer. Further, such a process has another disadvantage in using a raw material very difficult to obtain. In the case of polymers having repeating units of the formula (5), 4-chloro-4'-mercaptobenzophenone (which is very difficult to obtain) is used as a raw material.
On the other hand, there is also known a process for producing these crystalline aromatic polyketones by Friedel-Crafts polymerization. In such a case, when the polymerization is carried out in a conventional organic solvent, polymers having a low molecular weight can only be obtained.
For example, diphenyl ether and terephthaloyl chloride are polymerized in a solvent of nitrobenzene using aluminum trichloride as a catalyst to give a low molecular weight polymer having an inherent viscosity of 0.13 (U.S. Pat. No. 3,065,205).
But the use of anhydrous hydrogen fluoride as a solvent makes it possible to produce a polymer having a high inherent viscosity for the first time. That is, a high molecular weight crystalline polyketone is obtained by using anhydrous hydrogen fluoride as a solvent and boron trifluoride as a catalyst (U.S. Pat. No. 3,442,857).
In addition, the crystalline aromatic polyketones having the repeating units of the formula (1) produced by Friedel-Crafts polymerization are lower in modulus at a temperature of about 200.degree. C. to about 350.degree. C. and smaller in both the heat of crystallization and the heat of fusion than the polymers having repeating units of the formula (1) polymerized by polycondensation with nucleophilic substitution. Further, nuclear magnetic resonance spectra show that the polymer obtained by Friedel-Crafts polymerization has spectra due to ortho-and/or meta-position arrangement in addition to paraposition arrangement. Therefore, the polymer obtained by Friedel-Crafts polymerization is low in crystallinity due to the different structure of ortho and/or meta substitution and is lowered in modulus (Japanese Patent Unexamined Publication No. 155228/85).
The same example can be seen in aromatic polysulfones obtained by Friedel-Crafts polymerization. That is, in the polymer obtained from diphenyl ether and 4,4'-bis(chlorosulfonyl)diphenyl ether, about 20% of ortho orientation (that is, different bonding) is present [Polymer 6, 589 (1965)].
As mentioned above, it is very difficult to obtain polymers having uniform structure, a high melting point and high crystallinity by the Friedel-Crafts polymerization.
On the other hand, there has been known no process for producing crystalline aromatic polythioetherketones by using easily available raw materials and simple process steps, and even if crystalline aromatic polythioetherketones are produced, they cannot be used practically as a heat resistant polymer material due to their low molecular weights.